Engine/Message 2.0 and beyond

Insert Message 2.0 description here (Krista will get to this ASAP)

As for what we do when addressee lists contain non-pEp addressees:

11:52 < fdik> darthmama: for all p≡p addressees, we want to have p≡p message 2.0, without 
              exception
11:52 < fdik> darthmama: we'll make a hard cut here
11:53 < fdik> darthmama: for non-p≡p addressees, we never use it
11:53 < fdik> darthmama: without transport system, when there is at least one non-p≡p. 
              addressee in recipients, then we'll don't use p≡p message 2.0
11:53 < fdik> darthmama: with transport system, we will have a split then
11:54 < fdik> darthmama: this should be documented, beginning with copying these lines  
              into a wiki page, please

More soon.